I have sit there for more that three hours to make a compare between the seamaster and sea-dweller, but now I still can't decide which one is really better. I was confused. When I get this question, I began to be lost in my early days. In the years since my previous comparison, Omega has created a new dive watch - the Seamaster Planet Ocean. Inside and out, the Planet Ocean is watch with specifications which exceed those of the previous generation Seamaster Professional. While the Seamaster Professional is a watch that compares well with the Rolex Submariner, the Planet Ocean is more appropriately compared to Rolex's true deep-sea diving tool watch - the Sea-Dweller.
I have spent a very long time to study the two watches, and I get a rough answer:
TOTAL POINTS POSSIBLE: 90
SEAMASTER PLANET OCEAN TOTAL POINTS: 74.5
SEA-DWELLER TOTAL POINTS: 76.5
 
TOTAL NUMBER OF CATEGORIES: 9
TOTAL CATEGORIES TIED: 0
TOTAL CATEGORIES SEAMASTER: 4
TOTAL CATEGORIES SEA-DWELLER: 5
Given that I purchased the Sea-Dweller and not the Planet Ocean, I recognize a degree of inherit bias on my part in evaluating these two watches. Still, only two points separate these two great watches.
If I am asked privately which one is better, my answer is Seamaster Professional from Omega. For me, the PO is just too darn big in the 45.5mm size, I don't like the flat black dial, I don't care for the hands, and the double AR coated crystal is an absolute deal breaker for me.  I loved the polished accents on the Seamaster Professional bracelet, and I loved the distinctive shape of the scalloped bezel.
In my opinion, the Sea-Dweller is an absolute timeless classic, more aesthetically pleasing, and a much stronger diving tool than the Planet Ocean. No matter which type of the two you prefer, I would congratulate to you on your right choice. You have chosen a wonder not only a time piece but a miracle of the wolrd.